Academy of Diagnostic & Osteopathic Medicine
MUSCLE
Muscles are located throughout the body, attached to bones, lining organs, and forming the heart. There are three types of muscle: skeletal muscle, which is striated and voluntary; smooth muscle, which is non-striated and involuntary; and cardiac muscle, which is striated and involuntary. Muscles are supplied with blood by local arteries, such as the femoral artery for leg muscles, and venous drainage occurs through local veins, which return blood to the systemic circulation. The functions of muscle vary: skeletal muscles enable movement, smooth muscles control the function of organs like the intestines, and cardiac muscle pumps blood throughout the body. Common conditions include muscle strains, where muscle fibers are overstretched or torn, and myopathy, which refers to diseases that weaken or impair muscle function.
TENDONS
Tendons are located throughout the body, connecting muscles to bones. They are made of dense connective tissue, primarily consisting of collagen fibers, which give them strength and elasticity. Tendons are supplied by blood vessels from the surrounding muscles or bones, and venous drainage occurs through accompanying veins. The main function of tendons is to transmit the force generated by muscle contractions to bones, enabling movement. Common tendon issues include tendonitis, which is inflammation caused by overuse or injury, and tendon ruptures, which are complete tears that may require surgical intervention.
NERVES
Nerves are found throughout the body, forming a network that connects the central nervous system, or CNS, to peripheral tissues. Each nerve is made up of axons, which carry electrical signals, and is surrounded by protective connective tissue layers called the endoneurium, perineurium, and epineurium. Nerves are nourished by tiny blood vessels called vasa nervorum, and venous drainage occurs into local veins. The primary role of nerves is to transmit sensory signals from the body to the CNS and motor signals from the CNS to the body, enabling movement and sensation. Common nerve-related conditions include neuropathy, which is nerve damage that causes pain, numbness, or weakness, and nerve compression, such as carpal tunnel syndrome, where pressure on a nerve disrupts its function."
BONES
Bones form the skeletal framework of the body. Each bone consists of compact bone on the exterior, spongy bone in the interior, and a marrow cavity in the center. Bones are covered by a thin outer layer called the periosteum. Bones receive blood through nutrient arteries, which enter the bone via small openings called foramina, and venous drainage occurs through venous sinuses into the systemic veins. The main functions of bones include providing structure to the body, protecting vital organs, enabling movement by serving as attachment points for muscles, and producing blood cells in the bone marrow. Common bone-related conditions include osteoporosis, which is the loss of bone density and strength, and fractures, which are breaks in the bone caused by trauma or stress.
LIGAMENTS
Ligaments are found at joints, where they connect bones to other bones. They are made of dense connective tissue, primarily composed of collagen fibers, which makes them strong and resistant to stretching. Blood supply to ligaments comes from small vessels in the surrounding tissues, and venous drainage occurs into local veins. The primary function of ligaments is to stabilize joints and limit excessive movement to prevent injury. Common ligament injuries include sprains, where the ligament is overstretched or partially torn, and complete ligament tears, which often require surgical repair.
TISSUES
Now let’s talk about tissues. The body is made up of four main types of tissue, each with a unique function: Epithelial Tissue: This tissue forms a protective layer. It covers surfaces like your skin and lines internal cavities, such as your digestive tract. Connective Tissue: This tissue provides structure and support. Examples include bone, cartilage, and even blood, which is a specialized connective tissue. Muscle Tissue: Muscle tissue is what enables movement. It comes in three forms: skeletal muscle, which moves your body voluntarily; smooth muscle, which controls movements in organs like the intestines; and cardiac muscle, which keeps your heart beating. Nervous Tissue: This tissue transmits electrical signals throughout the body. It’s found in your brain, spinal cord, and nerves, and it allows you to respond to stimuli, think, and control your movements. Each of these tissues plays a vital role in keeping your body healthy and functioning efficiently.
CARTILAGE
Cartilage is the body’s built-in shock absorber—a smooth, flexible connective tissue that cushions joints, supports structures like the nose and ears, and provides a framework for bone growth. Unlike other tissues, cartilage has no blood supply, meaning it heals slowly when damaged. Over time, wear and tear can break it down, leading to conditions like osteoarthritis. Keeping cartilage healthy requires movement, hydration, and the right nutrients, like collagen and glucosamine. It’s the body's natural padding, protecting joints and keeping motion smooth and pain-free.
BRAIN
The brain is housed within the cranial cavity of the skull, where it is protected by meninges and cushioned by cerebrospinal fluid. It is divided into three main parts: the cerebrum, responsible for higher cognitive functions and voluntary movement; the cerebellum, which coordinates balance and fine motor skills; and the brainstem, which controls vital autonomic functions like breathing and heart rate. The brain receives oxygenated blood from the internal carotid and vertebral arteries, which form the Circle of Willis. Venous drainage occurs through the dural venous sinuses, which empty into the internal jugular veins. The brain controls sensory input, motor functions, cognition, emotions, and autonomic processes, making it the command center of the body. Pathologies include stroke, caused by an interruption of blood supply leading to brain tissue damage, and traumatic brain injury (TBI), resulting from external forces that can impair cognitive and motor functions.
SPINE
Spinal Cord: The Body’s Information Highway The spinal cord is a long, cylindrical structure running from the brainstem down the vertebral column, enclosed within the spine for protection. It acts as the main communication pathway between the brain and the rest of the body. The spinal cord is divided into cervical, thoracic, lumbar, sacral, and coccygeal regions, each controlling different body functions. Blood supply comes from the anterior spinal artery and paired posterior spinal arteries, with venous drainage into the spinal venous plexus. Its function is to relay sensory and motor signals between the brain and peripheral nerves, allowing movement, reflexes, and sensation. It also controls automatic reflex responses, like pulling away from heat. Common issues include spinal cord injuries, which can cause paralysis, herniated discs, pressing on nerves and causing pain, and spinal stenosis, a narrowing that leads to nerve compression.
PERIPHERAL NERVOUS
The Peripheral Nervous System, or PNS, is your body's communication highway, carrying messages between the brain, spinal cord, and the rest of your body. It’s divided into two main branches: the somatic nervous system, which controls voluntary movements like walking or picking up a cup, and the autonomic nervous system, which manages involuntary functions like heart rate and digestion. The PNS is what allows you to feel pain, move your muscles, and react to the world around you. Without it, your brain would be isolated, unable to control the body it was designed to command.
AUTONOMIC NERVOUS
The Autonomic Nervous System, or ANS, is the part of your nervous system that runs on autopilot, keeping you alive without you even thinking about it. It controls your heartbeat, breathing, digestion, and even pupil dilation. It has two branches: the sympathetic nervous system, which kicks in during stress—think "fight or flight"—and the parasympathetic nervous system, which helps you relax and recover. Whether you're running from danger or digesting a meal, the ANS is working 24/7 to keep your body balanced and functioning.
NEUROTRANSMITTERS
Neurotransmitters are the body's chemical messengers, responsible for everything from mood to muscle movement. Dopamine is the brain’s reward chemical, controlling pleasure, motivation, and movement—too little can lead to Parkinson’s, too much can contribute to addiction. Serotonin is your mood stabilizer, regulating happiness, sleep, and appetite—low levels are linked to depression. Acetylcholine is essential for learning, memory, and muscle function—without it, you wouldn’t be able to move or think properly. These chemicals are the signals that keep your brain and body in sync.
BLOOD BRAIN BARRIER
The Blood-Brain Barrier is your brain’s personal security system. Made of tightly packed cells, it protects the brain from harmful substances in the bloodstream while allowing essential nutrients, oxygen, and hormones to pass through. This barrier keeps out bacteria, toxins, and even some medications, making brain infections rare but also making it difficult to treat neurological diseases. It’s the ultimate gatekeeper, shielding the most important organ in your body from potential threats.